Poly(arylene sulfide) (herein below, it may abbreviated as “PAS”) represented by poly(phenylene sulfide) (herein below, it may be abbreviated as “PPS”) are engineering plastics excellent in heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical properties, dimensional stability, and the like. The PAS is commonly used in a wide variety of technical fields such as electrical and electronic equipments, automotive equipments, and packaging materials because it can be formed or molded into various kinds of molded or produced products, films, sheets, fibers, etc. by general melt processing techniques such as extrusion molding, injection molding, or compression molding.
As a typical production process of a PAS, the process, in which a sulfur source is reacted with a dihalogenated aromatic compound in an organic amide solvent such as N-methyl-2-pyrrolidone (herein below, it may be abbreviated as “NMP”) under heating condition, is known. As the sulfur source, an alkali metal sulfide, an alkali metal hydrogen sulfide, or a mixture thereof is generally used. When an alkali metal hydrogen sulfide is used as the sulfur source, the alkali metal hydrogen sulfide is used in combination with an alkali metal hydroxide.
Since polymerization of PAS is performed at high temperature, a byproduct sulfur compound resulting from a raw material or a product resulting from decomposition of an organic amide solvent used as a reaction solvent may become a cause of malodor.
Thus, after being separated from a reaction liquid containing the polymer thus produced, PAS produced by polymerization is purified by washing with water, an organic solvent, or a mixture liquid of water and the organic solvent. However, even after the washing treatment, there is still a case in which the occurrence of malodor upon production and molding of PAS is not completely inhibited.
Further, a separated liquid containing the organic amide solvent that is obtained after separation of PAS from the reaction liquid containing the polymer produced and also a separated liquid consisting of a wash waste liquid that is obtained after carrying out washing PAS by using the aforementioned organic solvent or the like may contain a byproduct sulfur compound resulting from a raw material or a product resulting from decomposition of an organic amide solvent used as a reaction solvent, or an organic solvent used for the washing as a cause of malodor. Accordingly, an enormous effort is required for a treatment of deodorizing them, and it remains as an obstacle for reusing the organic amide solvent, washing solvent, or the like.
The organic amide solvent, washing solvent and the like are recycled through a common distillation treatment. However, as the cause of malodor cannot be completely removed even after the distillation treatment, occurrence of malodor upon the production and molding of PAS remains unavoidable when PAS is produced by using the recycled organic amide solvent or washing solvent.
Japanese Patent Application Laid-Open (JP-A) No. 2005-194312 (Patent Literature 1, which corresponds to US 2007/0161777 A1 and EP 1702943 A1) discloses a process for producing PAS including washing the PAS obtained by polymerization with a hydrophilic organic solvent such as acetone containing water in an amount of 1 to 30% by mass to have a nitrogen content of 50 ppm or less based on the mass of the polymer, by which adhesion onto a mold or a die is significantly reduced upon melt molding. JP-A No. 2005-225931 (Patent Literature 2, which corresponds to US 2007/0093642 A1 and EP 1714994 A1) discloses a process for producing PAS with high whiteness and excellent melt stability including washing the polymer produced in a polymerization step repeatedly with a washing liquid consisting of water, a hydrophilic organic solvent such as acetone or a mixture solvent thereof, washing it in a final step with water or the mixture liquid to control the washing condition such that pH of the washing liquid obtained after washing is in the range of 8.0 to 11.0, and removing an organic amide solvent, alkali metal halides, oligomers, and decomposition products adhered onto PAS after separation treatment. Meanwhile, WO 2004/060973 A1 (Patent Literature 3, which corresponds to US 2006/0086374 A1 and EP 1577337 A1) discloses a process for producing PAS including washing the polymer separated from the reaction liquid with an organic solvent such as acetone and then distilling the recovered organic solvent after adding an inorganic acid such as hydrochloric acid to reduce the content of an alkali compound like methyl amine, that is presumed to be derived from decomposition of an organic amide solvent.
All the inventions disclosed in Patent Documents 1 to 3, however, did not succeed in inhibiting completely an occurrence of malodor during production and molding at high temperature such as melt molding of PAS. Further, all the inventions disclosed in Patent Documents 1 to 3 cannot avoid an enormous effort required for a deodorizing treatment of a byproduct sulfur compound of a raw material for causing malodor, which is contained in a liquid containing an organic amide solvent obtained after separation of PAS from the reaction liquid or a wash waste liquid obtained after washing PAS with an organic solvent, an organic amide solvent as a reaction solvent, or a decomposed product of an organic solvent used for the washing.